There exist, at present, various techniques of gripping or holding fibres in twisting members of ringless spinning apparatus, determining the design of the fibre-gripping device. Thus, there are employed twisting members comprising a cylindrical housing with blades on the side surface thereof, supporting a disc with a through-going passage for the advancement of fibres, and a fibre-gripping device including a spring-biased sleeve accommodated within the housing coaxially therewith; however, the performance of these members is characterized by a relatively high rate of yarn breakage due to the fact that the yarn is being formed from individual fibres which display low cohesion to one another until they are twisted into the yarn, and if the degree of twist defining the strength of the yarn proves to be insufficient, breakage takes place. The degree of twist, in its turn, is mainly dependent on the technique and effort of gripping the fibres in the twisting member, i.e. it is ultimately dependent on the design of the fibre-gripping device.
The requirements put before the gripping of fibres in the twisting member are such that, on the one hand, the gripping effort should be sufficient to impart to the fibres the necessary twist and to produce yarn of adequate strength, while, on the other hand, the effort should not be excessive, so that the formed yarn could pass through the gripping device either freely or with the necessary tension, so as to avoid the production of overtwisted yarn necessitating the addition of several extra operations in its further processing.
There is known a twisting member of a ringless spinning apparatus, comprising a cylindrical housing with blades on the side surface thereof, supporting a disc with a through-going axial passage for the advance of fibres, and a fibre-gripping device including gripping elements and a spring-biased sleeve accommodated within the housing coaxially therewith. One of the gripping elements is in the form of a ball received partly in a recess made in the end of the spring-biased sleeve and urged by this sleeve against the axial passage of the disc, the latter acting as the second gripping element (cf. SU Inventor's Certificate No. 484,269; Int.Cl..sup.3 DO1H 1/12, filed in 1973).
This twisting member is distinguished in that the gripping of fibres by the ball takes place simultaneously in two zones, i.e. the first one between the disc and the ball and the second one between the ball and the sleeve. The existence of the two gripping zones gives rise to considerable resistance to the propagation of the twist through the axial passage of the disc toward the outer surface thereof where the process of joining the fibres to the end of the yarn takes place, so that the process is prone to instability, the fibres are poorly twisted intermediate the two gripping zones, and in case of some impurity or a strand of unseparated fibres coming in, the joining process is interrupted, and breakage occurs.
There is further known a twisting member basically similar to the above/described one, wherein the passage through the disc extends eccentrically and at an inclination angle with respect to the axis of the disc, so that the ball is urged against the disc without closing the outlet of this through-going passage (cf. SU Inventor's Certificate No. 941,445; Int.Cl..sup.3 DO1H 7/885, dated 1982).
This twisting member is devoid of the gripping zone between the disc and the ball, which provides for easier propagation of the twist into the fibre-joining zone, and for a reduced breakage rate. However, should a piece of impurity or a strand of unseparated fibres find its way into the fibre-advancing passage and thus step up the yarn tension, the ball can be pushed away from its socket and driven by centrifugal forces toward the periphery of the disc, which, firstly, affects the gripping of fibres between the spring-biased sleeve and the ball, thus leading to the yield of substandard yarn, and, secondly, unbalances the twisting member, thus causing vibration and rapid wear of its bearings.
There is further known a twisting member of a ringless yarn-spinning apparatus, likewise comprising a cylindrical housing with blades on the side surface thereof, supporting a disc with an eccentrically extending passage for the advance of fibres, and a fibre-gripping device with two gripping elements, including a spring-biased sleeve mounted in the housing coaxially therewith (cf. SU Inventor's Certificate No. 630,615; Int.Cl..sup.3 DO1H 1/12, published in 1978).
In this twisting member one of the gripping elements is in the form of a projection on the disc shaped as a body of revolution concentric with the disc, the passage in the disc also extending through the projection. The other gripping element is the end face of the spring-biased sleeve, urged against the projection.
The last-described twisting member provides for obtaining yarn of a higher quality, owing to the stable gripping of fibres, and for avoiding vibration at higher speeds in the operation of the apparatus.
However, the increased distance from the zone of joining the fibres to the yarn on the outer surface of the disc to the fibre-gripping zone, due to the extended length of the through passage in the disc and its projection, affects the control over the fibres in this portion of the path of the yarn, and of shorter fibres, in particular. In other words, over such a prolonged portion commensurate with the fibre length, the probability of reliable gripping and spinning-in of a fibre at both ends--one end in the joining zone and other end in the gripping zone--is seriously impaired, and when one end of a certain fibre is loosely engaged, the fibre is prone to become separated from the bulk of the fibres by the air stream moving through the twisting member and to be carried away. Consequently, a large proportion of fibres, particularly, shorter ones, is carried into the waste, which affects the yield of yarn. Furthermore, the "fast" gripping of the fibres between the projection and the sleeve results in the leaping tension of the yarn when a piece of impurity or a strand of fibres enters the gripping zone, causing yarn breakage.
It should also be mentioned that the manufacture of a twisting member with a stationary projection on the inner surface of the disc and a channel extending through the disc and the projection involves a relatively complicated procedure, as long as the popular technique of making parts of this kind is casting with subsequent machining.